The present invention relates to a polybenzazole article having markedly superior light resistance, which is preferable as industrial materials, and to a production method thereof.
Polybenzazole fiber has at least twice the strength and elastic modulus of p-aramide fiber and is a typical commercially available super fiber at the moment. In addition, it has a limiting oxygen index of 68 and high heat resistance to stand decomposition temperatures of up to 650xc2x0 C. Thus, the fiber is expected to be a next generation super fiber.
Production of articles from a polyphosphoric acid solution of polybenzazole polymer has been known. For example, production conditions are disclosed in U.S. Pat. No. 5,296,185 and U.S. Pat. No. 5,385,702, water washing and drying method is disclosed in WO 94/04726, and heat treatment is disclosed in U.S. Pat. No. 5,296,185.
While polybenzazole articles have extremely advantageous properties as industrial materials, as mentioned earlier, once physically damaged, their light resistance becomes lower. In particular, when they are exposed to a light in the visible region, they show lower strength. As used herein, the physical damage includes bending and kink band caused by shear force. The kink band is observed as a black band under a microscope of 200 magnification. An article free of physical damage does not show any significant decrease in strength upon exposure to sunlight, but is susceptible to damage during, for example, weaving a fiber, knitting a fiber or processing a fiber to give various products. Therefore, the present inventors have intensively studied to give a polybenzazole article, which is light, highly strong, and which has high elastic modulus, high heat resistance, and high light resistance.
Accordingly, the present invention provides a polybenzazole article superior in light resistance, which comprises a polybenzazole and a light-resisting agent that allows for a regular reflectance of the article of not more than 30% in not less than 30% of the wavelength region of from 450 nm to 700 nm. Preferably, the present invention provides the above-mentioned polybenzazole article, wherein the light-resisting agent allows for a regular reflectance of the article of not more than 20% in not less than 10% of the wavelength region of from 450 nm to 700 nm, the above-mentioned polybenzazole article having a strength of not less than 35 g/d, the above-mentioned polybenzazole article wherein the light-resisting agent is an oxidation dyestuff, the above-mentioned polybenzazole article wherein the light-resisting agent is an aromatic amine compound or phenol, and the above-mentioned polybenzazole article wherein the light-resisting agent is added in a proportion of 0.01% to 20.0% by weight of the article.
The production method of the present invention comprises extruding a polybenzazole solution, extracting a solvent, and adding a light-resisting agent to an article before drying, whereby to give a polybenzazole article superior in light resistance. Further, it is the above-mentioned production method of a polybenzazole article having superior light resistance, wherein the light-resisting agent is added to the article in not longer than 10 minutes.